astroengine writes: "Something besides volcanic eruptions and asteroid and comet impacts has sculpted the surface of Mercury — an unknown process, possibly still going on today, that causes the ground to swell from the inside out. The evidence, collected by NASA's MESSENGER spacecraft currently orbiting the innermost planet, is scattered all over Mercury, including a dramatic finding that half of the floor of the biggest crater on the planet has been raised above the walls.

The MESSENGER's team findings were announced at the Lunar and Planetary Science Conference in Houston on Wednesday and will be published in this week's Science."